Our modern civilization cannot be sustained without burning carbonaceous materials for primarily motive and electrical power within the foreseeable future. The carbon dioxide (CO2) generated by such burning may be contributing to the gradual increase of the planet's temperature since 1900. This is occurring because CO2 permits the sun's energy to pass through the atmosphere, but traps the longer wavelength energy radiated by the earth into the atmosphere.
The integrated plants and processes of this invention can help reduce the amount of CO2 currently vented into the air as a by-product of synthesizing the various products later discussed in the description of the manufacturing plant flow diagrams. Consequently, the reduction of CO2, which is a greenhouse gas, through the sequestration processes detailed herein, reduces the amount of greenhouse gases vented into the atmosphere. Further, the plants of this invention produce substantial energy savings by balancing exothermic and endothermic reactors as discussed below.
U.S. Pat. No. 6,306,917 to Mark S. Bohn et al. teaches that hydrocarbons, carbon dioxide, and electric power can be manufactured at a plant using the Fischer-Tropsch (FT) reactors. It also suggests that urea can be produced from the carbon dioxide but no suggestion is given as to what facilities or processes are needed to manufacture the urea or the economic practicality of such a course. U.S. Pat. No. 6,632,846 to Sheppard et al. teaches that ammonia, carbon dioxide, hydrocarbons, electric power and urea can be manufactured using FT reactors. Urea is produced from reacting the ammonia with the carbon dioxide.
In U.S. Pat. No. 4,886,651, Patel et al. describe an integrated system that produces methanol, ammonia, and higher alcohols from natural gas. Steam reformers are used to produce streams of gases rich in hydrogen. Nitrogen for the ammonia synthesis is obtained from an air separation unit. The process is not relevant to a coal or petroleum coke feedstock.
In U.S. Pat. No. 6,248,794, Gieskes describes an integrated process for converting hydrocarbon gas to liquids. The tail gases from the Fischer-Tropsch reactor are used only as fuel. Also, the systems described are not relevant to systems using a solid carbonaceous feedstock.
In U.S. Patent Application Publication No. 2002/0143219, Price et al. describe a system for converting natural gas to hydrocarbons and ammonia. Tail gases from a FT reactor are recycled to the front end to a reformer in one example, and tail gases are recycled back to a second autothermal reformer in another example. Here again, solid carbonaceous feedstocks requiring gasification cannot be used in this system.
In U.S. Pat. No. 6,586,480, Zhou et al. describe an integrated system using synthesis gas derived from coal for producing hydrocarbon liquids and ammonia. In this system, the FT tail gas is shifted and hydrogen removed from the shifted tail gases is used in ammonia production. Reforming the gaseous hydrocarbons in the FT tail gases is not considered.
The mentioned references deal with economic niches where tax incentives, regulatory penalties and other incentives must combine with other factors to make the processes commercial. A continuing increase in world temperatures or a firmer tie-in between the CO2 in the atmosphere and increasing world climate temperatures could quickly result in such incentives. The plants can be of particular utility when sited at remote locations where there is a large surplus of natural gas, petroleum, coal or other carbonaceous materials which are presently unrecoverable because of transportation costs, etc.
Increasing regulatory demands have limited, and, in some instances extinguished, the petroleum producers' and refiners' ability to flare waste gases. Further, there are often limitations on the amounts and kinds of other wastes that can be disposed of locally without harm to the environment, e.g., at an offshore crude oil producing platform. The multi-product plants of this invention provide a mechanism for packaging the various unit processes required for the utilization of this invention in a manner that the resulting plants can be utilized to supply electricity for a platform, eliminate the need for flares, convert the waste gases and liquids normally flared into liquid hydrocarbons and ammonia substantially eliminating local CO2 emissions. Solid commercial products can also be produced for agriculture, e.g., sulfur.
The unit processes of this invention are each individually well known and the economics of the processes have been commercially proven. However, the joining of these unit processes as taught herein provides a utility for environmental and other purposes that has heretofore been unforeseen.